In the Applicant's European Patent Application Publication No. EP 1 878 920 A1, a solenoid-operated reagent dosing pump is described. Such a pump is typically used to supply a reagent, such as a reducing agent, via a nozzle, for dispersion into an exhaust gas stream within an exhaust pipe of a vehicle. This arrangement can be useful as part of a selective catalytic reduction system (SCR) for reducing harmful exhaust gas emissions from vehicle engines.
In some cases, it is desirable to mount a pump directly on the exhaust pipe, so that an output nozzle of the pump extends through a port in the exhaust pipe for delivery of the reagent to the exhaust gas stream. The pump must be attached securely to the exhaust pipe, and in such a way that there is no leakage of exhaust gases through the port.
The Applicant's European Patent Application No. 08169996.9 (“EP 08169996.9”), which is incorporated herein by reference, provides a pump mounting arrangement comprising: a boss attached or attachable to an exhaust pipe, and retaining means for retaining the pump in the boss, in use, wherein the retaining means comprises interfacial O-rings for damping vibration of the pump. The O-rings ensure that there is no rigid or stiff mechanical connection between the pump and the mounting boss or the exhaust.
Because the O-rings, located in an interfacial region between the pump and boss, are non-rigid, vibrations from the reciprocating solenoid within the pump are transmitted to the exhaust pipe to a lesser degree than would otherwise be the case. Instead, the vibrations are damped by the O-rings, so that the pump is acoustically decoupled from the exhaust pipe. Consequently, the operating noise of the pump is not appreciably amplified by the exhaust pipe when the pump is in use.
The O-rings also serve to reduce heat transfer by conduction from the exhaust pipe to the pump, for example when the O-rings are of a polymeric material such as rubber. Thus, in this case, the pump is, to an extent, also thermally decoupled from the exhaust pipe. This helps to reduce the amount of cooling of the pump and reagent required for efficient and reliable operation of the pump.
When a portion of the output nozzle of a dosing pump or other dosing device is positioned within the bore of an exhaust pipe, the output nozzle is subject to heating from the hot exhaust gases that flow through the pipe when the engine is in use. As well as reducing heat transfer by conduction from the walls of the exhaust pipe, it is therefore also desirable to minimise the heating effect of the hot gas stream on the output nozzle.
Against the above background, the present invention has been devised to further improve the design of a fluid dosing device and the mounting arrangement for a reagent dosing device in an exhaust pipe, for example in terms of durability and heat transfer reduction.